This invention relates generally to carburetors and more particularly to a throttle valve assembly for a carburetor.
Current throttle valves for carburetors have a metallic cam plate fastened tot to a metal shaft extending into the carburetor body and upon which a valve head is fixed to control the flow of air through the carburetor in response to rotation of the valve head. The cam plate is engageable with one or more stops on the carburetor body to limit rotation of the throttle valve assembly between idle and wide open throttle positions. The cam plate, shaft and valve head are machined and plated stamped parts. The cam plate is attached to the shaft with either a threaded fastener or by swaging over a portion of the shaft extending through the cam plate. The valve head may be a disc, such as in a butterfly-type valve arrangement, with the disc attached to the shaft with a threaded fastener. The machined or stamped components are relatively expensive to produce. Further, the use of threaded fasteners to connect the valve head to the shaft, and the cam plate to the shaft or the swaging of the shaft onto the cam plate greatly increases the cost, difficulty, time and labor required to assemble the throttle valve assembly.
Some carburetors have choke valves which may be closed to restrict the flow of air through the carburetor to facilitate starting of an associated engine. The choke valve may have a metal shaft extending into the carburetor body and a metal valve disc attached thereto by a threaded fastener which is received in and rotatable in the fuel and air mixing passage of the carburetor. The valve disc is rotated between a closed position substantially restricting air flow past the valve disc and an open position permitting a substantially unrestricted flow of air through the fuel and air mixing passage. Some choke valves have a plastic one-piece shaft with an integral handle which may be grasped by a user and rotated to move the choke valve between its open and closed positions. The valve disc may be press-fit into a slot formed through the shaft.
A carburetor with a throttle valve assembly having a plastic cam body connected to a plastic shaft which extends into the carburetor body and a valve head received in a slot formed through the plastic shaft. Desirably, the valve assembly eliminates the use of threaded fasteners and the need to swage or otherwise deform any of the components to connect them together. Desirably, the shaft and cam body are constructed and arranged to prevent relative rotation between them. This permits accurate location of the cam body on the shaft and facilitates calibration of the throttle valve assembly between its idle and wide open throttle positions. Further, the characteristics of the throttle valve assembly can be changed by simply providing a cam body having a different shape or construction with the shaft or valve head being the same for a wide range of carburetors. Still further, the slot in the shaft is preferably longer than the diameter of the valve head so that the valve head may shift axially on the shaft so that it is self-centering within the fuel and air mixing passage. The valve head can preferably also shift laterally relative to the shaft. This greatly facilitates assembly and manufacture of the throttle valve assembly by greatly increasing the tolerances with respect to the location of the valve head on the valve shaft and of the slot receiving the valve head.
Objects, features and advantages of this invention include providing a valve assembly which utilizes a plastic cam body connected to a plastic shaft, permits different cam bodies to be used with the same shaft and valve disc for different carburetors, self-centers and assures smooth movement of the valve disc within the fuel and air mixing passage, is lightweight and inexpensive to manufacture and assemble, eliminates the use of machined or stamped metal components for at least the shaft and cam body, eliminates the use of threaded fasteners or mechanical deformation such as swaging to connect components together, has improved corrosion resistant characteristics, reduces the time and cost to assemble the throttle valve assembly into a carburetor, is reliable, durable, rugged and in service has a long, useful life.